Radio direction finding system



,5, J. w. GREIG ET AL 1,922,677

RADIO DIRECTION FINDING SYSTEM Filed Oct. 15, 1931 3 Sheets-Sheet 2 RAD/A TI .1 W. GRE/G. 1 INVENTORSA. a. BA/LEY %TWW A TTORNEY Aug. 15,1933, J, w, ai A 1,922,677

RADIO DIRECTION FINDING SYSTEM Filed Oct. 15, 1951' asheets-sneet s ATTOQNE'Y Patented Aug. 15, 1933 a I UNITED "STATES PATENT" "OFFICE RADIO DIRECTION FINDINGSYSTEM John W. Greig, Little Falls, N. J., and Arnold'B.

Bailey, New York, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a Corporation of New York Application October 15, 1 931. Serial No. 568,903 13 Claims. (o1. 250-11),

This invention relates to methods of, or means sure effective, modulation at the mobile station for, radio direction finding and more especial between the received waves in a system in which ly to directive finding systems in which modua carrier wave and side'band frequencies. are lated waves and carrier waves are transmitted independently transmitted from the beaconsta- 5 from a'iixed or 'radio beacon station for the tion for direction finding purposes. 6o purpose 'of enabling a pilot at a mobile stalt is still another object of'this invention to tion. such as 'an aircraftto determine'his posienable'a pilot to differentiate between the varition with respect'to the beacon station. ous courses associated with v a radio beacon In certain direction finding systems in use station. I, e 10 at the present time which utilize a transmitter Accordingfto one embodiment of vthis in-, 65 at the-fixed or beacon station and a receiver Vention five antennae are employed at the beaat the mobile station, the pilot determines his con station, fourbeing positioned at the corners course-"from the phase relation between two of a square as, for example, the north, south, sets of waves transmitted from the beacon staeast and west corners, andthe fifth beingcention. One phase discriminating system in which tr'allylocated with respect to. these antenna. 70 v a rotating beam i s'used to introduce the de1- Side. band frequencies with suppressed carrier sired phase-space characteristic is disclosed in areradiated from the diagonally opposite an-,-

Patent 1,815,246 to 'Englund. In this and" in tennae, the modulation for one such pair of ansimilar systems a beam 'comprisingarotating' tennaa being'diiferent in frequency or phase or single side bound and a non-directional carrier continuity from that used for the other pair. 75 is transmitted and, at the mobile station. the The. currents supplied to the diagonally, oppolow frequency component obtained by combin-' site antennm are l80 outv of phase with each ing these waves is compared as to phase with other so that" tlae side tband frequencies raa similarcomponent obtained from anon-didiated in opposi e direc ionsare o 'opposite' 5 rectional side'band and a non-directional carphase. A carrier wave is radiated by the central rier also transmitted from the beacon station. non-directional antenna which wave is in phase I For purposes of accuracy and better modulaquadrature with the carrier used inthe production.- and for other reasons as discussed below; tion of, the side band frequencies. I he last it is clearly desirable in such a system-to emmentioned carrier is preferably suppressed. 30 ploy double instead of single side bands and At the mobile station, the carrier and the 85 this invention is particularly suitable-for use in side band frequencies radiated from one pair of r such a systemfor transmitting rotatingvdouble' antenna, say the east-west antennas, are co m side band frequencies and a non-directional carbined to reproduce the original audio frequency rier wave having a special phase relation with envelope whose phase is dependent upon the the side band frequencies so that modulation phase of the side band frequencies. The phase 90 at the mobile station is easily effected. relation, th 'at is, the phase similarity or opposi In a somewhat different type of system the tion as determined at themobile station, between intensities of two bi-lateral waves transmitted the'reproduced audioenvelope and the envelope from a beacon station in directions perpendiradiated from one, say the east, antenna of the 40 a 0 e cho h r a e mp rde there e n said pair indicates theposition, east or west, of 95 ire ion-5 D 8 ermine, courses a e the mobile station Lfrom the beacon station. which Pilot P 8 n plfeceives Similarlyfth'e north-south position of the mobile the Same {ndlcatmng o 'ie i nstation is jdetermined from the other, differently tage of thls systgm t a h p11t must modulated, 1 side, band frequencies. When the i 2 2; kgowledget .P w 53? inventionis employed in conjunction with the o 9P 0 sum-385.5 y. four-course system referred to above, or with' navigate the aircraft andlt-1S clearly desirable similar 8 stems the various courses ma be in such a system to provide-a differentindicad g tion for each of the courses associated with the" gg i i g z mor'e understood beacon station. 105 It one object f this, inventionto provide from'the following description taken in connec- =means for determining the direction of a radio 1311 Wlth the'drawmgsln w i p q 1 beacon in a more eflicient manner than hereto- Fig 1 illustrates a Tadlo beacon transmitter fore practiced. employed in one embodiment of the invention;

55 It is another object, of this invention to in Fig. '2 illustrates a receiver at the mobile sta- 110 the connections being such that oppositely 2 designate vertical antennapositioned respectively, at (say) the north and south corners'of a square and numerals 3 and 4 denote vertical antenna positioned, respectively, at the east and west corners of the square.

Reference numeral 6 designates a radio frequency oscillator generating a wave of frequency F1 and connected to balancedmodulators 7 and 8. Numeral 9 designates a low frequency oscillator generating a wave of frequency F2 and connected tobalanced modulator 7; and numeral 10 denotes a low frequency oscillator generatinga wave of frequency F3 and connected to balanced modulator 8. Balanced modulator '1 is inductively associated with antenna 1 and 2 by means of transformers 11 and 12, respectively,

phased currents are suppliedjto antenna land 2. Similarly, balanced modulator 8 is inductively associated with antenna 3 and 4 by means of transformers 13 and 14, respectively, the'connections for the two antenna being reversed; Reference numeral 15 denotes a 90 phase shifter connected to oscillator 6 and inductivelyassoci- .ated with antenna 5 through transformer 16.

In Fig. 2 reference numeral 1'7 denotes a receiving antenna which is associated with the receiver 18 by means of transformer 19. Two synchroscopes 20 and 21 are cor inec ted, respec-- tively, through filters 22 and 23 to the receiver 18, the filter 22 being adjusted to pass only currents of frequency F2 and filter 23'b'eing adjusted to pass only currents of frequency F3. Reference numeral 24 designates a low frequency oscillator generating a frequency F2 inphase with the cur rent generated at the transmitter in low frequency oscillator 9. Numeral 25 designates a low frequency oscillator which generates a wave'of frequency F3, this wave being in phase with the current generated at the transmitter in low frequency oscillator 10. Oscillator 24 isassociated with synchroscope 20 and oscillator 25' is connected to synchroscope 21.v ,A system for supplying eachsynchroscope with current synchronous with that generated in oscillators 9 and 10 is described in Englund Patent 1,815,246 supra.

The operation of the direction finding-system comprising the transmitter shown in Fig.v

1 and the receiver shown in Fig. 2 may be briefly described as follows. Referring to Fig; 1 side band waves F1F2 andF1+F2 with negligible carrier are supplied in opposite phase relation to antenna land 2. Sideuband waves F1-.F3 and F1+F3 with suppressed or negligible carrier are supplied througntransformers, 13 and 14 to antenna 3wand 4, -respectively,,and in opposite phase relation. A carrier wave shifted approximately 90 by means of phase shifter 15, with respect to that employed in producing the above side band frequencies is supplied through transformerv 16 to antenna 5. This earrier is designated on the drawings by 90 F1. Since the side band frequencies in .relative.

Numeral 5 de notes a vertical antenna positioned at the center of the square.

4 and 5 is shown.

the north antenna are reversed in phase from those in the south antenna as shown by the designations F1Fz. F1+F2 and 180 (Fr-F2), 180 (Fl+F2) on the drawings the resultant radiation in the north direction will have an audio frequency envelope which is in reverse phaseto that in the south direction. The phase designations on the drawings are, of course, only Similarly the double side band radiation in the west direction will be in a sense reversed inphase from that in the east direction as indicated on the drawings. It is this difference in phase in the opposite directions which provides the means of distinguishing between the various directions. This may be more clearly understood from a consideration of the vector diagrams shown in Figs. 3A, 3-B and 3C.

In Fig. 3A a plan view of antenna 1, 2, 3, For convenience only the waves radiated from the east, west and central antenna, that is, antenna 3,v 4 and'5, are'considered. The carrier supplied to modulator 8 in Fig. 1 is shown by vector (law at antenna 5. The upper and lower' side band frequencies in the eastantenna are represented by vectors Sm and San and the same side bands in the west antenna are represented by Srw and Szw. The vectors CE and Cw show the relative phase which the carrier would have in these, antenna if it were not suppressed. It should be noted that the two sideband vectors are symmetrical about the carrier vector so that their vector sum is in phase with the carrier. This condition is necessaryfor effective demodulation at the fundamental audio frequency. Vector C shows the'carrier current in the center antenna. No side bands are supplied to this antenna and the phase of this carrier is adjusted by means of phase shifter 15 to be in quadrature to thephase of the vectors CE and Cw. Assuming the feed line causes a phase shift of 30 vector'CE lags vector CEW by 30 and vector Cw of opposite phase with respect to CE is retarded a similar amount. Consequentlyveetor C is adjusted to lag the position it would have if there were no phase shift over the feed line.

Now consider any distant point P1 in space, as shown in Fig. 3-+C, chosen for convenience at a distance which is an integral multiple. of a wave length from the center antenna 5. Any other distance would only produce a rotation of the vectors without changing their relation to each other. Fig. 13-0 shows the vector S12 leading by 15 its position at-the east antenna and the vector Siw lagging by 15 its position at the west antenna, the lead and lag being due to the difierence in distance along the path between the receiver and the antenna 3, 4 and 5. It will-be seen that the sum S1w+s of the vectors Srw and Sm at point P1 is in quadrature to the position .ofthe component vectors at the antenna Band 4. Furthermore, the sum S2W+E of the side band vectors Saw and S213 is in quadrature to the position of these component vectorsat these same antenna. It may be stated, therefore, that if two like antenna are excited in opposite phase by equal currents, the vector sum at a remote point in space at a, distance an integral number of wave lengths from the center of the antenna system will be in phase quadrature to the currents in the two antenme. The carrier wave C arrives at point P1 without effective phasechange and, since its vector is symmetrical with respect to the vector sums of the side band radiations, it is in proper phase .to produce eifective-modulatiom More specifically, at the point Pi the resultant of the side band vector sums S1W+'e, and S2W+E is in phase with the carrier vector. 7.

If thedistant pointis nearer to therwest antenna than to the east .antenna as shown by point P2 in Fig. 13-3 the carrier and side band components, when demodulated, will produce an audio frequency opposite in phase to that produced at point P1. e

Thus in Fig. 3-;B 'vector -S1w leads by 15 its position at antenna-land vector'Sm lags by 15 its position at antenna 3. Similarly vector Szw leads by 15 itsposition at :antennatand vector S a lags by 15 its positionat antenna 3. The carrier vector. C. is symmetricalvwith respect to the side band vector. sums S1w+aand S2W+E and it is 180 out of phasewith the instantaneous vector .resultant of the side 'band vector sums. Referring to Fig. 2 the position of the, mobile station is determined'in the following manner. The two sets of double side bands and the quadraturecarrier are received and demodulated in receiver 18. The phase of the low frequency modulation component F3 intheoutput of filter 23, obtained by demodulation inlreceiver .18 of the double side bands FiiFsradiated by'antennm 3 and 4 and the carrier F1; is com.- pared in synchroscope 21 with the phase of the reference current established by oscillator 25, the waves generated byoscillator 25 beingin phase with those generated ,in oscillator 10. A similar phase indication .indicates that the mobile station is east of the beacon station and an opposite phase indication denotes that'the mobile station'is west of the beacon station. Ina similar manner, but utilizing the side bandsradiated by antenna: 1 and 2, theaposition ofthe mobile station, north or south; with respect: to

the beacon station is indicated bysynchroscope Fig. 4 is a directive diagram for a radio beacon system in whichthe intensities of two directive waves are compared for direction finding purposes. Such 'a system is described in the article Development of the Visual-Type Airway Radio BeaconSystem 'byMessrs. J. H. Dellinger, H. Diamond, and S. W. Dumnore,- published in the Proceedings of the Institute of Radio Engineers for May, 1930. In asystem having a directive diagram similar to that shown in- Fig. 4 there are four courses along which the pilot of a mobile station-receives the same indication. By means of the present; invention the several'courses may easilybe distinguished. The directive diagram for such a combined system is showninFig.5.

The transmitting and receiving apparatus employed in the combined system for determining. both a particular course to the beacon and the bearings of the mobile station with respect to the beacon may be separate and distinct, orthe equipment shown in Figs. 1 and 2 for" determining the direction to the beaconmay bemodified so as to give a course'indication to the pilot. By adjusting oscillators 9' and .10 'in- Fig. 1 to generate suitable frequencies as, for example, 65. cycles and 85 cycles, respectively, and connecting between the output terminals of filters 22 and 23 in Fig. 2 avisual indicator comprising vibrating reeds tuned to' these two frequencies the intensities of the two setsof modulated waves transmitted from the'beacon station may be compared. The pilot, by observing the visual modulator 8 by means of transformer 40.

3 indicator, may follow one of l,tlie four courses shown in Fig. 5 and, by noting the indication of synchroscopes 20 and 21, hemay easily determine which of the four courses he is following. The antenna system shown inFig. 6 is similar to that shown in Fig. 1 except that no in'di vidual central antenna isemployed, an equivalent effect, however, being achieved bythe conjoint use of the other antenna. Reference numerals. 26,27, 28 and 29 designate vertical antenme positionedatthe. corners of the square and numerals '30, 31,;32and ,33.,denote terminating impedances connected between the ground and these antenna respectively. Reference numeral 34 designates a transformer, the primary winding of which is associated with the balanced modulator 7 and the secondary Winding of which is, associated with the diagonallyopposite antenna 39 and 3,1, one terminal an impedance connected across the output of the phase shifter 15. The midpoint of the secondary windings-of transformers 34 and 35 are adjustably connected to impedance 36. 'I-he antenna system shownjin Fig. fi produces the same. directive diagram as that shown in Fig.1. The double side bands Fr-Fz and F.1+F2

in-=the output of modulator 7 ,are. supplied through transformer 34 and impedances 30 and '31- to :the radiating antenna: 26 and 27 in opposite phase relation, the carrier being suppressed. similarlythe side bands"F1-Fa and F1+Fr from balanced modulator 8 are supplied through transformers 35 to antennae 28: and 29 in opposite phaserelation. Quadrature. carrier currents from the phase shifter-.15 are supplied through winding '36 and the secondary winding of transformers 34 and 35 to'the antennae 26,

27g '28 and 29 in phase so that non-directional radiation of the quadrature carrier occurs;

The antenna system' of Figs." 7 and 8 both of which employ crossed loops instead of four-vertical antennaearevery similar, the chief differe'nce being that thequadrature carrier; 1 is =radiated from the loops in the system shownin Fig. 8, the entire structure acting as a. simple vertical antenna as in Fig. 6 while in the'system bf Fig. 7 an individual antenna is used for that purpose. 1 In Fig. 7 reference numerals 37 and 38 designate two crossed loops positioned at right angles to each other, loop 37 being associated with modulator '7' by means of transformer 39 and loop 38 being. associated with A vertical-antenna 41 centrally located with. respect to the two loops is associated with the .phaseshifter'15 by means of stransformerxiz.

In'Fig. *8 reference numerals 43 and 44 designate two crossed loops similar to those shown in Fig. 7, loop 43' being associated with modulator 7 by means of transformer 45 and loops 44 being associated with modulator 8- by means of transformer 46. Reference numeral 47 designates a' transformer, the primary" winding of whichis connected to the output of phase shifter 15 and the secondary windingof which has one terminal grounded and the other terminal connected to the midpoints of the secondary windings of transformers 45 and 46; Y

oppositely-phased double side band waves FitFz are radiated from the vertical portions of lo'op 37 in Fig. 7 and loop 43 in Fig. 8; and oppositely-phased 'double side band waves FliFS are radiated from the' vertical portions of loop 38 in Fig. land loop 44 in Fig. 8. In Fig. 7 the quadrature carrier waves supplied from phase shifter "through transformer 42 to antenna 41 is radiated non-directionally from antenna 41 and in F'ig. 8 thequadraturecarrier' currents induced-in the secondary winding of transformer 47 are supplied through the secondarywindings 'of transformers 45 and '46 to the loops 4 4 and 45'so that thequadrature'carrie'r' current is radiated non-directionally.

Although the-invention has been described in connection'with certain-antenna arrangements mitting non-directionally a carrier wave-sub and other apparatus it isnot to be limited to such arrangements-andapparatus and-it is to be understood that other antenna systems and apparatus may be employed in carrying out the invention without exceeding its scope.

- What isclaimed' is:

1..In a radio system, means for transmitting bi-laterally "double side'band waves, and means for transmitting non directionally a carrier wave in quadrature to that employed for producing the side bands.

2. In a radio'system, means for transmitting bi-laterally double side band waveswith suppressed carrier, means for transmitting bi-laterally' and at an angle to the first'transmission different double side band'waves with suppressed carrier, and means for producing'and transst'antially in-phase quadratureto the carriers employed for producingthe double side band 3. In a radio system, antenna, structure for transmitting 'a carrier wave of a particular wave length and double side bandwaves with negligible vcarrier comprising-a plurality of elements spaceda fraction of said wave length, andmeans for energizing at least two of said elements with double side band currents of oppositephase and said .structurewith carrier current in quadrature with thenegligible carrier.

4. In a radio system, four radiating elements positioned at the corners of a square, means conof diagonally opposite elewithdouble nected to onepair ments for energizing said elements side band currents of opposite phase, means connected to the other pairof elements for energizing said elements with different double side band currents of opposite phase, and ,means connected'to the elements forsupplying carrier currentin quadrature. to the carriers employed in producing the side bands. V

1 5. In a radio system, four radiating elements positioned at thecorners of a square, means connected to one pair of diagonally opposite eleelements with double nected to' the other pair of elements forener gizingrsaid elements with different double side band currentsof opposite phase, another radiating element, and means connected to said last mentioned element. forsupplying carrier current in quadrature to the carrier employed for producing the side'band currents.

6. In a radio system,'two crossed loops positioned atright'angles to each other, means connected to one loop'for energizing the vertical positioned at the corners of the square, a source of radio frequency energy, a source of low frequency energy, a-balanced modulator connected to said sources, the output terminals of said modulator'being connected to one pair of diagonally opposite elements, a second source of low frequency energy, a second balanced modulator connected tdthe'second source of low frequency energy and the source of radio frequency energy, the second balanced modulator having its output terminals connected to the other pair of elements, another radiating element positioned at the-center of the square and connected to" the radio frequency source, and wave shifting means included betweenthe radio frequen'cysource and the last mentioned radio element.

' '8. In a radio .system, four radiating elements frequency en'ergy and the source of radio frequency'energy, the second balanced modulator :having its output terminals connected to the other pair of elements, a phase shifter connected to the radio frequency source, said phase shifter having one output terminal connected to the radiating elements andv its other terminal associated with ground.

9. In a direction finding system, two spaced elements radiating bi-laterally oppositely-phased side band waves,,said elements also radiating a non-directional carrier wave in quadrature to the carrier, waves employed for producing ,the

side band waves, arnobile wave receiving means comprising a modulator, means associated with the modulator for comparing thephase direction of the'low frequency current in the modulator output andthe side band-envelope of the currentin one of the elements. I

10.1n a direction-finding system, a beacon station comprising four radiating elements,

-means connected to, one pair of diagonally oppositeelements for energizing said elements, with oppositely-phased modulated waves comprising a carrier andoa low frequency current, means connected to the other pair of elements for-energizing said elements with oppositely-phased modulated wavescomprising a carrier and a second low frequency current, means connected to the elements for producing a nondirectional carrier wave in quadrature to the carriers employed in producing the modulated waves, a mobile receiving station comprising means for demodulat- ,ing the waves received from the beacon station,

means for comparing the phase direction of the low frequency current obtained from demodulation of thefirstsetof modulated waves and the modulated envelope of the current in one of the first pair. of elements, means for comparing the phase directionof the low frequency current 0btained from demodulation of the" second set of modulated waves and the modulated envelope of the current in one of the second pair of elements.

11. In a radio system, means for producing a double side band with negligible carrier, transmitting means connected thereto for radiating bi-laterally said band, and means connected to the transmitting means for producing a carrier in quadrature to the negligible carrier as radiated.

12. In a bearing determining system, means for producing a double side band with negligible carrier and a carrier in quadrature with the negligible carrier, a plurality of-radiators connected thereto and arranged to transmit in opposite phase each single side band and non-directionally the quadrature carrier, and means for receiving and modulating said double band and quadrature carrier.

'as employedin producing the double side band and for comparing the intensities of the dissimilar low frequency components.

, JOHN W. GREIG.

ARNOLD B. BAILEY. 

